Polymerization of conjugated dienes and monovinyl aromatic compounds with multifunctional polymerization initiators

ABSTRACT

AN IMPROVED MULTIFUNCTIONAL POLYMERIZATION IS PREPARED IN A TWO STEP PROCESS BY REACTING AN ORGANOMONOLITHIUM COMPOUND WITH A POLYMERIZABLE ADDITIVE AND THEN CONTACTING THE REACTION MIXTURE WITH A POLYVINYL AROMATIC COMPOUND.

United States Patent 3,644,322 POLYMERIZATION 0F CONJUGATED DIENES ANDMONOVINYL AROMATIC COMPOUNDS WITH MULTIFUNCTIONAL POLYMERIZA- TIONINITIATORS Ralph C. Farrar, Bartlesville, Okla., assignor to PhillipsPetroleum Company No Drawing. Filed Feb. 3, 1969, Ser. No. 796,204

Int. Cl. C08d 1/32; C08f 1/74, 7/04 U.S. Cl. 260-943 8 Claims ABSTRACTOF THE DISCLOSURE An improved multifunctional polymerization is preparedin a two step process by reacting an organomonolithium compound With apolymerizable additive and then contacting the reaction mixture with apolyvinyl aromatic compound.

This invention relates to an improved multifunctional polymerizationinitiator. In another aspect, it relates to an improved process forpolymerizing conjugated dienes or monovinyl-substituted aromaticcompounds and mixtures thereof. In another aspect, it relates to animproved polymerization process for employing lower initiator levels toproduce a polymeric product with a desired Mooney viscosity value. Instill another aspect, it relates to a process for producing hydrocarbonsoluble and stable polylithium initiators.

Many dilithium polymerization initiators are well known to the art, butmany of these known compounds are not soluble in hydrocarbons, oftenrequire a polar diluent for their preparation, and are not suflicientlystable that they can be prepared and stored for very long periods andstill retain their activity. They must, therefore, often be prepared andused within a relatively short time.

Multifunctional polymerization initiators can be prepared from anorganomonolithium compound, a polyvinyl aromatic compound and aconjugated diene or monovinyl aromatic compound by charging allingredients initially. By means of such a process, multifunctionalinitiators which are hydrocarbon soluble and stable can be prepared in ahydrocarbon diluent.

It has now been discovered that if the aforementioned multifunctionalpolymerization initiators are prepared in a two step process whichcomprises (1) reacting an organomonolthium compound with a conjugateddiene or a monovinyl aromatic additive and then, (2) adding thepolyvinyl aromatic compound to the reaction product formed in the firststep that an improved multifunctional polymerization initiator isproduced.

It is an object of this invention to provide an improved multifunctionallithium based initiator. It is an object of this invention to provide astable, hydrocarbon soluble initiator so asto enable easy storagethereof. It is still a further object to provide a process forcontrolling the Mooney viscosity of the polymers produced according tothis invention. Other objects, advantages, and features of my inventionwill be apparent to those skilled in the art from the followingdiscussion and examples herein set forth.

According to the present invention, stable initators containing at leasttwo carbon-lithium bonds are readily prepared. They are branched and thebranches are terminated with lithium substituents which serve asreaction sites for polymerization initiation. Branched polymers resultwhen polymerizations are initiated in the presence of thesemultifunctional polymerization initiators.

The multifunctional polymerization initator produced according to thisinvention can be employed at much lower initiator levels to produceproducts with the desired 3,644,322 Patented Feb. 22, 1972 Mooneyviscosity value than those initiators prepared when all initiatorcomponents are charged initially. Furthermore, when liquid products aredesired, initiators prepared according to this invention give lowermolecular weight products than are obtained from initiators that areprepared charging the several ingredients initially, and for a giveninitiator level, polymers produced with an initiator formed by chargingall of the ingredients initially have a much higher molecular weightthan when the initiators prepared according to the present invention areemployed.

The multifunctional polymerization initiators are prepared in a two stepprocess which comprises (1) reacting an organomonolithium compound witha polymerizable additive comprising a conjugated diene or amonovinylsubstituted aromatic compound using from 2 to 15 moles ofpolymerizable compound per mole of the organomonolithiurn compound, and(2) adding from 0.15 to 2 moles of polyvinyl aromatic compound per moleof the organomonothium compound and allowing suflicient time for it toreact with the reaction product formed in the first step.

In the first step of the process, an organomonolithium compound isreacted with the polymerizable additive in the presence of an inertdiluent.

Hydrocarbons or polar compounds can be employed as the diluent andmixtures of polar diluents and hydrocarbons can be employed if desired.Polar diluents are of particular value for the production of conjugateddiene polymers if a high vinyl content is desired as well as forpreparing random copolymers. Hydrocarbon diluents in cluding paraflins,cycloparaffins, and aromatics generally containing from 4 to 10 carbonatoms per molecule are suitable. Exemplary polar compounds includeethers, thio ethers, tertiary amines, and the like.

Those polymerizable additives utilized for initiator preparation aregenerally those conjugated dienes containing 4 or 5 carbon atoms permolecule such as 1,3-butadiene, piperylene or isoprene, andmonovinyl-substituted aromatic compounds such as styrene or alkylatedstyrenes containing from 8 to 20 and preferably 8-12 carbon atoms permolecule. Mixtures of these compounds can also be employed.

The organomonolithium compounds that are reacted with the polymerizableadditive in step one of this invention are represented by the formulaRLi; wherein R is an aliphatic, cycloaliphatic, or aromatic radical, orcombinations thereof, preferably containing from 2 to 20 carbon atomsper molecule. Exemplary of these organomonolithium compounds areethyllithium, n-propyllithium, isopropyllithium, n butyllithiurn,sec-butyllithium, tert octyllithium, n decyllithium, n eicosyllithium,phenyllithium, 2 naphthyllithium, 4 butylphenyllithium, 4 tolyllithium,4 phenyl-butyllithium, cyclohexyllithium, 3,5 di nheptylcyclohexyllithium, 4-cyclopentylbutyllithiurn, and the like. Thealkyllithium compounds are preferred for employment according to thisinvention, especially those wherein the alkyl group contains from 3 to10 carbon atoms.

The polyvinyl aromatic compounds that are employed in the second step ofthis process and which are added to the reaction product formed in thefirst step of my invention are those polyvinyl aromatic compounds thathave any of the following general formulas:

wherein Y is a vinyl group, and wherein each R is hydrogen or an alkylgroup containing from 1 to 4 carbon atoms with a total of the alkylsubstituents having not more than 12 carbon atoms, and wherein n is aninteger of 2 or 3. The vinyl substituents in the above formulas (b) and(c) can be on either or both rings. Exemplary of suitable polyvinylaromatic compounds are 1,2-divinylbenzene; 1,3-divinylbenzene;1,4-divinylbenzene; 1,2,4-tri-vinylbenzene; 1,3-divinyln'aphthalene;1,8-divinylnaphthalene; 1,3,5-trivinylnaphthalene; 2,4-divinylbiphenyl;

3,5 ,4'-trivinylbiphenyl; 1,2-divinyl-3,4-dimethylbenzene;

1,5 ,6-trivinyl-3,7 -diethylnaphthalene;1,3-divinyl-4,5,8-tributylnaphthalene;2,2-divinyl-4-ethyl-4'-propylbiphenyl;

and the like. Divinyl aromatic hydrocarbons containing up to 26 carbonatoms per molecule are preferred for employment according to thisinvention; particularly divinylbenzene in either its ortho, meta, orpara isomer and commercial divinylbenzene which is a mixture of saidisomers is also quite satisfactory.

As hereinbefore stated, the preparation of my initiators is conducted inthe presence of an inert diluent such as a hydrocarbon or polar diluent.The mole ratio of polymerizable additive to organomonolithium compoundis in the range of about 2:1 to :1, preferably in the range of about 4:1to 12:1. The mole ratio of polyvinyl aromatic compound toorganomonolithium compound is in the range of about 0.15:1 to 2:1,preferably in the range of about 0.25:1 to 1:1.

The temperature for preparing the initiators is generally in the rangeof about 85 F. to 300 F. The particular time employed for each step willgenerally depend upon the temperature employed and would be in the rangeof about 5 seconds to 24 hours for each step. In many instances, aperiod of less than an hour for each step gives satisfactory results. Itis to be understood that a longer reaction time would promote branchingin the initiator but an excess reaction period can lead to crosslinking,i.e., gel formation. If the initiator becomes gelled a polymer preparedin its presence will contain gel. It is thus evident that for a givenmole ratio of reactant, one skilled in the art can regulate temperatureand time in order to obtain a gel-free branched initiator.

The polymerizable additive employed for initiator preparation can all beadded in the first step or a portion can be added in the first step andthe remainder when the polyvinyl aromatic compound is added in thesecond step.

The polymers which can -be prepared using initiators of this inventionare homopolymers made from conjugated dienes containing from 4 to 12 andpreferably 4 to 8 carbon atoms per molecule; copolymers of 2 or moreconjugated dienes; homopolymers made from monovinylsubstituted aromaticcompounds containing 8 to and preferably 8-12 carbon atoms per molecule;copolymers of 2 or more monovinyl-substituted aromatic compounds; andcopolymers of conjugated dienes with monovinylsubstituted aromaticcompounds.

Homopolymers of conjugated dienes can range from low molecular weightliquids to solid rubbery polymers. Copolymers can be random or blockcopolymers. This invention provides a method for obtaining rubbery blockcopolymers of conjugated dienes and monovinyl-substituted aromaticcompounds that have high green tensile strength. Multiple blocks ofpolymerized monovinyl-substituted aromatic compounds are essential toobtaining polymers having high green tensile strength. Resinous blockcopolymers can be prepared when employing a predominant amount ofmonovinyl-substituted aromatic compound and a minor amount of conjugateddiene. High impact resins with a high degree of clarity and other goodproperties can be prepared using the multifunctional initiators of thisinvention. When compounded with ingredients known in the art, the lowmolecular weight polymers can be used as plasticizers, caulkingcompounds, sealants, potting compounds, coating compounds and the like;and the high molecular weight polymers have application in adhesivecompositions, shoe soles, floor tile, tire tread, hose, belting,gaskets, and the like.

The amount of initiator used in the polymerization process depends uponthe particular multifunctional polymerization initiator employed and thetype of polymer desired. An effective initiator level is normally in therange of about 0.25 to 100, preferably 1 to 50 milliequivalents oflithium per 100 grams of monomer (Mehm) charged to the polymerizationsystem.

The milliequivalents of lithium can be conveniently determined by analkalinity titration of a known volume of the reaction mixturecontaining the multifunctional initiator. Said alkalinity titrationemploys standardized acid, e.g., HCl, and an indicator such asphenolphthalein to determine the end-point of titration. The alkalinenormality thus obtained provides a value for the milliequivalents oflithium per milliliter of reaction mixture containing themultifunctional initiator. The alkalinity concentration (normality) thusdetermined is then employed for charging a known quantity ofmilliequivalents of lithium in polymerization recipes employing themultifunctional initiators of this invention.

It is preferred that the polymerization be conducted in the presence ofa suitable diluent such as benzene, toluene, xylene, cyclohexane,methylcyclohexane, n-butane, nhexane, n-heptane, isooctane, mixtures ofthese and the like. Generally, the diluent is selected fromhydrocarbons, i.e., parafiins, cycloparaflins, and aromatics containingfrom 4 to 10 carbon atoms per molecule.

Polymerization conditions generally known to the art can be suitablyemployed. The polymerization temperature can vary over a broad range andis generally about -100 to 300 F., and it is preferred to operate at atemperature of at least F.

When a polymerization is conducted in the presence of a multifunctionalinitiator of this invention, the unquenched polymerization mixture has abranched structure and the branches contain terminal lithium atoms.Treatment with various agents such as carbon dioxide, epoxy compounds,and the like, yield polymers with terminal functional groups, which havereplaced the lithium atoms, on the several polymer branches. Polymers ofthis type can be cured easily to form a tight network by reaction withvarious polyfunctional reagents. As an example, low molecular weightliquid polybutadiene containing multiple carboxy groups can be cured toa solid polymer with polyfunctional aziridinyl compound or apolyfunctional epoxy compound.

Illustrative of the foregoing discussion and not to be interpreted as alimitation on the materials herein employed or on the scope of myinvention, the following examples are provided.

EXAMPLE I Multifunctional polymerization initiators were prepared byreacting secondary-butyllithium, butadiene, and divinylbenzene. Therecipe was as follows:

Toluene, ml 1,3-butadiene, grams (0.17 moles) 9 Sec-butyllithium, g.mmoles 1 18 Divinylbenzene, g. mmoles 18 Temperature, F. 158 Total time,min 40 1 Gram millimoles.

The first initiator, hereinafter designated as initiator A, was preparedaccording to the invention. The butadiene,

Cyclohexane, parts by weight 760 1,3-butadiene, parts by weight 70Styrene, parts by weight 30 Initiator, meq. Li per 100 grams monomerVariable Temperature, F. 158 Time, hours 3 Cyclohexane was charged firstand the reactor was then purged with nitrogen. Butadiene was addedfollowed by the styrene and then the initiator. The temperature wasadjusted to 158 F. for the polymerization. After 3 hours a weightpercent solution of the antioxidant,2,2'-methylene-bis(4-methyl-6-tert-butylphenol), in a mixture of equalparts by volume of toluene and isopropyl alcohol was added. The amountof antioxidant solution added was suflicient to provide one part byweight of the antioxidant per 100 parts by weight of the polymer. Thepolymer was coagulated in isopropyl alcohol, separated, and dried.Quantitative monomer conversion was obtained in all runs. Inherentviscosity, gel. and Mooney value (MS-4 at 212 F.) were determined. Runs1 to 4 were made with Initiator A, runs 5 to 8, with Initiator B.Results were as follows:

1 Milliequivalents of lithium/100 grams monomer. 1 Determined accordingto U.S. 3,278,508, col. 20, notes (a) and (b). 8 ASTM D 1646-63.

These data show that polymers prepared using the initiator of theinvention had a much lower molecular weight for a given initiator level,as evidenced by inherent viscosity and Mooney viscosity data, than thosepolymers prepared using Initiator B. In other words, products with adesired Mooney value can be prepared with a much lower initiator levelwhen the initiator of the invention is used than can be obtained withInitiator B.

EXAMPLE II Two multifunctional initiators were prepared according tothis invention and one in which all initiator components were chargedinitially. Each of the initiators was then employed for thepolymerization of butadiene. At the conclusion of each polymerization,carbon dioxide was introduced for the purpose of producing carboxytelechelic polymers. Following the carbon dioxide treatment, eachreaction mixture was acidified with dilute hydrochloric acid and washedwith water to remove excess acid and initiator residues. Isopropylalcohol was added to clarify the solution. The polymer was recovered bystripping under vacuum in a stream of nitrogen at a temperature of about212 F. Recipes for preparing the initiators, polymeriza- 6 tion recipes,and results in terms of carboxy content, and poise viscosity of thepolymers were as follows:

Run

intiator preparation:

Ste 1' p 1,3-butadiene, parts by weight Cyeloheieane, parts byweightsec-Butyllithium, rnhm. Divinylbenzene, mhm. Temperature, F Time,minutes Step 2;

LEI-butadiene, parts by weight... Divinylbenzene, rnhm. Temperature, FTime, minutes Polymerization:

Step 3:

Gyclohexane, parts by weight- 1,3-butadiene, parts by weightTemperature, F. Time, minutes. Polymer properties:

Carboxy content, percent 2 Poise viscosity at 77 F.

system 1 Gram millimoles per grams total monomer in Lisieki, Analytical2 Based on the method of I. S. Fritz and N. M. Chemistry 23, 589 (1951).

3 Brookfield Synehro-Lectn'c viscometer, Model RVF.

4 0.18 mole.

5 0.37 mole.

The-products from the three runs were liquids but those from runs 1 and2, i.e., prepared according to the invention, had a lower molecularweight (poise viscosity) than the product from Run 3.

EXAMPLE III Run Polymer sample, grams 5 5 Chromium 2-ethylhexoate, grams0.032 0. 034 Epon 828, grams 0. 335 0.332 Gel, percent 49 21 The aboveExamples II and 7.111 effectively demonstrate production of a polymerinitiated with the multifunctional initiator of this invention and thecuring of these branched polymers to a tight polymer network.

As will be evident to those skilled in the art, various modifications ofthis invention can be made or followed, in light of the discussion anddisclosure herein set forth, without departing from the scope and spiritthereof.

I claim:

1. A polymerization process comprising polymerizing at least onepolymerizable monomer wherein said polymerizable monomer is a conjugateddiene containing from 4 to 12 carbon atoms per molecule,monovinyl-substituted aromatic compound containing from 8 to 20 carbonatoms per molecule, or mixture thereof, under polymerization conditionsat a temperature in the range of about 100 to 300 F, employing amultifunctional organolithium polymerization initiator in the range ofabout 0.25 to 100 milliequivalents of lithium per 100 grams ofpolymerizable monomer charged to said polymerization process,

wherein said multifunctional polymerization initiator is that preparedby the process comprising:

(a) reacting an organomonolithium compound with a polymerizable additivein the presence of an inert diluent,

wherein said polymerizable additive is a conjugated diene containing 4or 5 carbon atoms per molecule, a monovinyl-substituted aromatic com- R(6-11) Rni-n w 1 in u wherein y is a vinyl group and each R is hydrogenor alkyl containing from 1 to 4 carbon atoms such that the total of allalkyl substituents contains not more than 12 carbon atoms, 11 is aninteger of 2 or 3, and

wherein the mole ratio of said polymerizable additive to saidorganomonolithium compound RLi is in the range of about 2:1 to :1 andthe mole ratio of said polyvinyl aromatic compound to said organolithiumcompound RLi is in the range of about 0.15:1 to 2: 1.

2. The process of claim 1 including treatment of the resulting polymertherein produced with carbon dioxide or epoxy compounds to yieldpolymers with terminal func tional groups.

3, The process as defined in claim 1 wherein said polymerizable monomeris a conjugated diene containing from 4 to 12 carbon atoms per molecule,or said mixture thereof with said monovinyl-substituted aromaticcompound containing from 8 to carbon atoms per molecule; and

wherein in said step (a) said polymerizable additive is said conjugateddiene containing 4 or 5 carbon atoms per molecule.

4. The process of claim 3 wherein the mole ratio of said polymerizableadditive to said organomonolithium compound RLi is in the range of about4:1 to 12: 1, the mole ratio of said polyvinyl aromatic compound to saidorganomonolithium compound RLi is in the range of about 0.25:1 to 1:1,and said steps (a) and (b) are conducted at a temperature in the rangeof about F. to 300 F. for a time of about 5 seconds to 24 hours per eachof said steps (a) and (b).

5. The process of claim 4 wherein said organomonolithium compound issec-butyllithium, wherein said po1ymerizable additive is butadiene, andwherein said polyvinylsubstituted aromatic compound is divinylbenzene,and wherein said process is conducted in the presence of a diluent oftoluene or cyclohexane, and wherein said polymerization temperature isat least 85 F., and wherein the concentration of said initiator is inthe range of about 1 to 50 milliequivalents of lithium per grams ofmonomer charged to the polymerization system.

6. The process of claim 2 wherein said inert diluent is a hydrocarbon orpolar compound or mixture thereof, and where hydrocarbon is paraffin,cycloparaflin, or aromatic, containing from 4 to 10 carbon atoms permolecule, and where polar is ether, thioether, or tertiary amine.

7. The process of claim 4 wherein a portion of said polymerizableadditive further is employed in said step (b), such that a portion ofsaid polymerizable additive is employed in each of said steps (a) and(b).

8 The process of claim 6 wherein said polymerization process isconducted in the presence of a hydrocarbon diluent, and said hydrocarbondiluent is a parafiin, cycloparaflin, aromatic, or mixture thereof,compound containing from 4 to 10 carbon atoms per molecule.

References Cited UNITED STATES PATENTS 3,135,716 6/1964 Uraneck et a1.26094.2 M 3,157,604 11/1964 Strobel 260-94.2 M 3,280,084 10/1966Zelinski et al. 26094.2

JAMES A. SEIDLECK, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE I 17755 LHC CERTIFICATE OF CORREGI'IONPatent No. 3,64h,322 Ralph c. Farrar Dated February 22, 191

It is certified that error appears the above-identified patent and thatsa Letters Patent are hereby corrected as shown below: I

Claim 6, column 8, line 19 (line 1 of claim 6), after "claim" and before"wherein" delete "2" and insert Signed and sealed this 18th day of July1 972. I

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

